


Noire's Cosplay Secret

by PaddedPriestess



Category: Hyperdimension Neptunia
Genre: Diaper, Gen, Soiling, Wetting, messing
Language: English
Status: Completed
Published: 2018-12-01
Updated: 2018-12-01
Packaged: 2019-09-05 08:25:14
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 1,356
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16807021
Author URL: https://archiveofourown.org/users/PaddedPriestess/pseuds/PaddedPriestess
Summary: Uni talks to Neptune, who unwittingly gives away a secret about her older sister that might be a bit hard to believe.





	Noire's Cosplay Secret

Neptune sat in her lofty seat/bean bag, mashing away furiously at her controls. All she needed was one more lap, just one more, and she would win. “Come on… You… Graah, outta my way!” She shouted, throwing her shoulder to the side as if she were in the vehicle presented on screen. “Just… 10 more… Come on…” She bit her lip. So close! Just about…

“Neptune!”

“Waaah!” The violet haired CPU shouted, jerked out of her game by the sudden interruption. Of course, that momentary lapse meant she lost her place in the game, and she soon jumped from first to at least 5th place. “Aaagh… Uni, you totally killed my 7 race streeeeak.” She whined out.

“I’m sure you’ll be fine, Neptune. Anyway, Nepgear and I needed a game. That Planeptune one that came out last weekend? Whatever it was called, we wanna play it.” She walked closer, looking over the games stacked next to the console Neptune was playing. Of course, as she got near it, she also noticed the color palette of the floor change. It got darker the closer to Neptune it was. It also looked oddly… Yellow?

“Oh, gross! Neptune, did you pee yourself again!?” Uni groaned out. Noire had warned her about this bad habit, and sure enough, the evidence was splattered all over the floor. “H-hey! Don’t say it like that! I just… Helped color the floor? Ehehe…” She laughed nervously, rubbing the back of her head.

“I can’t believe I actually doubted Noire on this. You really are just a big baby.” She sighs out, reaching down to grab the game she’d just spotted; it was the 2nd game under the stack. “Oh, pshaw! You think I’m a big baby? At least I don’t wear diapers like your loner of a sister!” She huffed, working to get back into her game.

“Wh-what!? Noire doesn’t wear diapers, you liar!” She shouted, perhaps a bit too loud. This was a silly argument to be having, and she didn’t want Nepgear to hear. “Does too! She- Err… Actually, yeah, you’re totally right. I made it up! Haha…” Neptune turned red in the face, directing her full attention back to the game; an unusually uncharacteristic response from the Planeptunian. “E-eh? You just… Oh, whatever.”

From there, she grabbed her game and went back to play with Nepgear, eager to see what this strange fish-boxing simulator was all about. However, even this strange game couldn’t keep her mind off of what Neptune had said. Did her sister really wear diapers? It was… Well, ridiculous! But something about how quickly the quirky girl had changed her outset seemed too familiar. It was like any other time Noire had been found out doing something embarrassing, and then made her swear to keep it with her life.

Of course, Neptune was never good at keeping secrets, so that kind of reaction happened a lot. That’s the only reason Uni even bothered to take this as anything more than a silly joke at her sister’s expense. But like that, it just… She had to find out for herself! Surely Noire would think she had some privacy since Uni was supposed to be in Planeptune for half the day. So, maybe if she went home a bit early, a little spying wouldn’t hurt…

Uni snuck into her basilicom, using the special entry tunnel that everybody apparently kept forgetting about. She didn’t want to risk other people alerting Noire about her coming home, so she had to be stealthy. Just like Sneaky Serpent, silently creeping through the halls…

Now, with Noire free for the day, there was one of two things she’d be doing; Working or cosplaying. And considering the fact that she was free to go to Planeptune, that meant there was probably no work. Hence, her tsun sister was probably in her bedroom, trying out new outfits. Walking quietly through the halls, she approached said bedroom, keeping her ears perked.

As expected, she could hear a quiet giggling. Her hunch was right! Tiptoeing up to the door, she carefully opened it, just the tiniest bit until she could see her sister. What she saw made her jaw drop.

Noire was in a cosplay outfit, that much was certain. It had a short skirt, a blouse, and a darkened palette; the colors of Lastation’s elementary school outfits. One of her sister’s favorites, so normally, it wouldn’t be surprising. No, what was surprising was the thick, poofy diaper that was obviously showing from underneath her skirt. She seemed to be posing in it as well, flipping up her skirt and turning around to shake her butt in the mirror.

The sight broke many, many pre-established thoughts about her sister. For one, Neptune was right for once. For two, no elementary school student wore diapers. For three, her sister was wearing a diaper! And she was modeling it!

Uni became lost in her thoughts over the situation, unable to fully comprehend the sight she was seeing. Her mind raced with so many things that suddenly made sense. That strange crinkling she’d hear randomly, those times she could’ve sworn she smelled… Well, something. It all finally clicked!

“Uh-ooooh~” Came a voice that broke Uni’s train of thought. Noire had just spoken to… The mirror? What was she doing? The young candidate focused her eyes on the mirror, trying to see just what her sister was up to. As had been happening for the past couple of minutes, the twintailed tsundere kept shaking her diapered butt in the mirror… But then she stopped.

“Gotta go poopy!” She shouted, causing Uni to turn red in the face. As if she was playing out some kind of scene in a play, Noire danced on her feet a bit, now holding her sides. “Uuugh… Gotta potty so bad…” She held herself a bit, some gas escaping as she did so. “I… I don’t think I can make it! Oh noooo!” She said in her best cutesy accent, suddenly hunching over so her butt was in full view of both the mirror and her sister.

Noire gave a quiet grunt, biting her lip and blushing bright red. Her sister’s face turned to one of complete shock as, something she could’ve never imagined prior to this moment being witnessed right before her eyes. The back of the CPU’s diaper began to bulge out, a sticky, squelchy sound coming from her rear end. She buckled down and pushed more, the brown mess continuing to pour out and absolutely stain the back panel of the padding, alongside just sagging it down to far below the skirt. A strange mixture of a sigh of relief and a lewd moan came from the stinky girl, her diaper starting to turn yellow in the front as a stream of urine flowed freely from her urethra, obviously taking its chance now that she’d emptied her bowels into her undergarment.

Finally, with the muffled hiss dying down, Noire gave one last grunt and shook her diaper in the mirror; it was now stained yellow and brown, hanging far below the bottom of her skirt. If she walked out anywhere, it wouldn’t be hard to tell that she was wearing a very, very used diaper. “Oopsies… I had a widdwe accident~” The goddess said to nobody in particular, sticking a hand on the back of her diaper and squishing the mess around. “Nnnn~ I’m such a naughty pottypants…” She giggled into the mirror, giving her butt a couple light spankings before standing upright.

Uni slowly closed the door, blinking and trying to rattle her brain to make it work. What had she just witnessed? Was that actually her sister? She couldn’t really move, moving her hand to her hip and giving her a quick pinch to make sure she was awake. Judging from the sharp sting her nails gave, she was indeed not dreaming. Noire was really doing all that! Shivering to herself, she made her way as distant as she could from her poopy diapered cosplaying sister. She’d need a bit of time to figure out how she felt about all of that…

**Works inspired by this one:**

  * [Uni's Discovery](https://archiveofourown.org/works/17466056) by [SilverWritingDesk](https://archiveofourown.org/users/SilverWritingDesk/pseuds/SilverWritingDesk)




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